8:00 PM - EN06.05.01
Toward a Structure-Properties Relationship Phase Diagram for Eumelanin Films
Anthony Camus1,Manuel Reali1,Jennifer MacLeod2,Alessandro Pezzella3,Clara Santato1
Polytechnique Montréal1,The University of Queensland2,Università degli Studi di Napoli Federico II3
Show Abstract
The charge transfer and transport properties of bio-sourced materials are complex, due to their chemical and structural composition. Their biosynthesis generates chemical heterogeneity, e.g. macromolecules resulting from more than one building block (monomer), and physical disorder, e.g. π-π stacked regions coexisting in the supramolecular structure. Chemical and physical disorder are key factors limiting the performance of organic electronics1–3. Among the plethora biomaterials available in nature, eumelanin, a black-brown bio-pigment of the melanin family, is an interesting candidate for study4–6. It is a redox-active7–10 quinone-based bio-macromolecule featuring electronic conjugation (alternating single and double Carbon bonds bonds), broadband UV-Vis absorption and hydration-dependent electrical response11–16. Eumelanin originates from the oxidative polymerization of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) monomers (building blocks). DHI and DHICA have several polymerization sites and co-exist in different redox states (fully reduced hydroquinone, semi-reduced semiquinone, and fully oxidized quinone). Therefore, eumelanin features chemical heterogeneity17–19. Monomers and oligomers generate several supramolecular structures, such that eumelanin also features physical disorder20. Recently, we showed that the early stages of DHI and DHICA films formation is driven by both chemical (covalent) and physical (self-assembly) interactions21. Particularly, self assembly of DHI is expected to deliver films featuring higher degree of pi-pi stacking with respect to DHICA, this last being a critical condition to the rational design of eumelanin-based functional devices22.
Herein, we investigate the role of oligomeric composition, relative humidity and type of solvent during DHI film processing. Preliminary results show that DHI films undergo to de-wetting23,24 or diffusion limited aggregation (DLA) phenomena25,26 depending on specific combination of solvent, relative humidity and molar mass distribution. Our investigation is a step forward to establish a phase diagram correlating film processing and structural properties of eumelanin films.
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